MORSE Guide

2. MORSE Guide

2.1. What does a simple MORSE network look like.

The following picture is used to give an initial idea about the
MORSE network. Information transmitted in the form of data packets comes from the connected
device A along the wire link to “radio” CU1. This “radio” is a
complicated piece of equipment that checks the packet, modifies it and
supplements it with records necessary for further transmission over the
radio channel. This is why it is labelled as a communication unit
(CU).

Fig. 2.1: Simple network MORSE

Amongst information added to the packet is the first section of
the route which the packet will travel through via the net environment to the destination CU3. In
our example CU3 is out of reach of
direct audibility of CU1, therefore the packet is routed through CU2.
This communication unit, as for all the others, is equipped with intelligence, which is used to take care
of the packet along the next section of its route. CU2 thus receives the
packet from CU1 and sends it on to CU3. This method of transmitting
packets can be called store and forward relaying. At the destination CU3
the packet is sent along the wire link to the external device B.

A radio network is generally more branched. Connection is made
between individual points in the direction of lines marked in the
drawing.

Besides these routes it is often possible to achieve connection by
further combinations, for example between CU3 and CU6. Whichever links
will be used during operation is determined by the quality of the
connection, according to loading of the network and according to the
structure of addresses used in the network. Each CU has information
about the choice of routes in its routing table (also store and forward
table) and according to these it then decides about routing obtained
packets.

Fig. 2.2: Branched network

2.2. MORSE addresses

Connection-oriented and Connection-less Transmission of
Data

The network can transmit data in two ways. For connection-oriented
transmission a route is created in advance by connecting individual
sections of the network and the route created is then available for
bi-directional transmission of data. An example is the telephone
network. This method is suitable for the transmission of a large amount
of data in one transmission. Other participants must wait during this
period.

The second method is connection-less transmission which is also
used in the MORSE network. Packets with data are sent to the network
here. Each packet is provided with the destination address and travels
through the network by itself. The length of the packet is limited to
1500 bytes, so transmission between two CU’s runs from 0.1 to 1 second
depending on the length of the packet and other conditions. Another
packet can then pass through the same section of the route to another
destination. The suitability of non-linked transmission for frequent
routing of short messages to a large number of participants comes from
this.

Non-linked transmission including addressing can be likened to the
postal service. In this case information is sent with the address of the
network of post offices which gradually regulate its progression to the
addressee. Let’s try and compare analogical terms:

Letter

Packet

Postal address

Packet header with address

Letter text

Data

Signature

CRC

Registered letter

Acknowledged receipt of packet

Letters can overtake each other

The same order of registered packets is not
guaranteed

Sorting of letters before delivery

Routing of packets

Address

The MORSE address contains 4 levels for
determining the destination in its 4 bytes. They are termed:

global - net - wide -
local

An example of an address is given
below:

690F0A11

It contains 4 bytes with each created from two hexadecimal
symbols:

69– global
(country specification, 69=CR, 6A=Slovakia…)

0F – net (area
in the country or other closer definition of the network)

0A – wide
(subnetwork, further specification)

11 – local
(specific CU user)

Each byte can acquire a value of 0 to 0xFF (0 to 255 dec), the
overall theoretical number of addresses is thus
2564 which is more than 4 billion. The
address architecture is important for the accessibility of individual
networks, especially at the remote supervision of the network
functionality. If not stated otherwise the MORSE address is recorded
using eight hexadecimal symbols.

The internal layout of the modem from the point of view of
configuration is contained in paragraph Communication unit.

2.3. Explanation of terms used

Packet

A packet is a sequence of bytes ordered according to precise
rules.

Fig. 2.3: Data packet

At the front of this sequence is a group of bytes which
contains basic information about the packet (type, length, who
determined for, etc) and this is called the head.

Behind this other bytes follow which carry necessary
information (data monitored by measuring devices, GPS position of
vehicle, text message, command for remotely operated pump etc.).
This part is labelled as data.

A packet is generally ended with a CRC which serves for data
integrity checking.

The particular form of the packet depends from the communication
protocol used.

What is the range of the MR400

The range or audibility of the radio signal in the 400 MHz band is
influenced by the shape of the terrain and other obstacles. Under
unfavourable conditions (city, valley) the range of the MR400 is several
hundred metres or several kilometres. Under favourable conditions
(direct visibility, good antenna) good quality operation is possible to
distances over 100 km.

Network Medium

The medium used for packet transmitting enables such broadcasting
of messages where the transmitted message can be picked up by more
receivers. Therefore the message must carry information about which of
the receivers must process it further. In our case it is the medium of
radio signals or the Ethernet network medium.

The other media type only allow signals to be transmitted between
two participants and can be called a link media. An example is the wire
communication line protocol RS232 which is used for the connection
between the CU and external devices.

Dispersed Intelligence

Operation in the network medium can be controlled in principle in
two ways:

The network can only contain one centre which controls routing of
messages, for example a telephone exchange. Participants then only
request the centre to mediate the routing of messages and the centre
undertakes everything necessary.

The second possibility is that the network is composed of elements
from which each is able to process the message in the necessary way.
This means deciding where the message should be routed and route it to
the appropriate channel (which here is the radio channel, Ethernet, wire
communication line, output port, service channel) and check the data
integrity. The MORSE system is composed of a CU equipped in this way.
All CU are the same and differ only in the setting of configuration
parameters. Therefore the MORSE network is easily expandable or
adjustable.